In the recent trend of advancement in downsizing and high performance of a variety of electronic apparatuses such as video tape recorders and personal computers, there is a demand for switches of small size, low profiling and high functional reliability for use in such applications as detecting presence or absence of storage media like tapes and disks, and operation of mechanisms such as knobs and doors.
Referring now to FIG. 5, description is provided of one such switch of the prior art. FIG. 5 is a sectional view of a conventional switch. In this figure, case 1 is made of an insulating resin in a box-like shape having an open top. A plurality of stationary contacts 2 made of an electrically conductive sheet metal are embedded in an inner bottom surface of case 1, and terminals (not shown) of these stationary contacts 2 are extended individually to the outside of case 1.
Lever 3 made of an insulating resin is housed inside case 1 in a manner so that it is swingable around fulcrum portion 31 at the left end, and it has actuating portion 32 of an upwardly protruding shape formed at the right end.
Movable contact 4 made of a flexible metal sheet is curved in the middle portion and it is housed inside case 1 with a small elastic flexure. Contact point 41 on one end of movable contact 4 is flexibly contacted with inner bottom surface of case 1, and stationary portion 42 at the other end is retained by projection 33 on the underside of lever 3.
In addition, cover 5 made of a thin metal sheet covers the upper opening of case 1, and actuating portion 32 of lever 3 protrudes upward from through hole 51 of cover 5.
The conventional switch of the structure shown here is so constructed that, first, movable contact 4 is inserted from the upper side into case 1 bearing stationary contacts 2 laid securely by such a method as insert molding in the inner bottom surface of the case 1, and lever 3 is then disposed inside case 1 such that projection 33 abutted against stationary portion 42 of movable contact 4 and bends movable contact 4.
Afterward, cover 5 is placed to close the upper opening of case 1 and fixed to the exterior wall of case 1 to complete assembly of the switch.
The switch assembled in this manner is mounted on a wiring board (not shown) provided with a wiring pattern, and the terminals of stationary contact 2 extending from case 1 are soldered to predetermined traces of the wiring pattern to establish electrical connections to an electronic circuit of an apparatus.
In the structure described above, lever 3 swings downward around fulcrum portion 31 when the portion of actuating portion 32 that protrudes above case 1 is pressed downward by any operation such as insertion or removal of a storage medium like a tape or a disk, or moving a knob or a door.
This makes the underside of actuating portion 32 depress the middle portion of movable contact 4, which in turn causes contact point 41 at the end of movable contact 4 to slide in a direction of stationary contacts 2 on the left side while maintaining its flexible contact with the inner bottom surface of case 1.
When actuating portion 32 is pressed a certain amount, contact point 41 comes into movable contact with stationary contacts 2. As a result, an electrical continuity is established among the plurality of stationary contacts 2 through movable contact 4.
When the pressing force on lever 3 is removed, lever 3 is thrust and swung back upward by a restoring force of movable contact 4. This causes contact point 41 to slide from stationary contacts 2 toward the right side while maintaining the flexible contact with the inner bottom surface of case 1, and return to the original position. As a result, the electrical continuity among the plurality of stationary contacts 2 is broken.
Japanese Patent Unexamined Publication, No. 2005-26035 is one example of the prior art references related to the present invention.
The prior art switch discussed above has a problem, however, that movable contact 4 is liable to become dislodged or deformed when being assembled since movable contact 4 is disposed in case 1 beforehand and lever 3 is placed inside case 1 while forcing movable contact 4 to bend, which also requires extra time for assembling.